The present invention relates generally to a foldable sofa-bed, davenport or the like having a sectionalized bed-frame which may be folded to one position to provide a sofa seat, and unfolded to an extended position to form a bed.
Foldable sofa-bed constructions of the aforementioned type are conventionally known and, as exemplified by U.S. Pat. No. 3,245,091, usually embody a mattress supporting flexible fabric structure or combination of flexible fabric structures on the foldable frame sections, to provide different flexible biasing characteristics in the seat forming section when in a folded position, and the body support section when in an extended bed forming position.
Basically, there are two important operating characteristics which should be considered with respect to the mattress supporting fabric, particularly in the folded seat forming section and the body supporting section in the unfolded and extended bed forming position. Thus, it is desirable that in the folded seat forming position, the mattress supporting fabric in the sections should cooperate in such a manner that the mattress-supporting fabric in the uppermost seat forming section should remain relatively taut, while in the other sections the supporting fabric should be relatively relaxed, in order to avoid upward crowning of the mattress in the seat forming section and the tendency to lift the seat cushions and thereby detract from the appearance of the sofa. In the extended bed forming position, it is desirable that the mattress supporting fabric, especially in the body or trunk section where most of the weight of a bed occupant is concentrated, should be maintained relatively as taut and firm as possible, and prevent sagging towards the center of the bed.
In the referenced patent, there is disclosed a structural arrangement which effectively addresses and eliminates the crowning effect in the folded seating position. However, in the presently known sofa sleeper mechanisms, the manufacturers have been unable to successfully achieve an acceptable degree of firm and non-sagging support for the mattress in an open bed position.
In the present invention, it is proposed to provide one or more transversely extending rigid rods or bars which are positioned below the mattress supporting fabric of the trunk or body frame section, and are supported at their end extremities by coiled springs which are relatively relaxed in the seat forming folded position. An actuating linkage is provided to laterally shift the rods or bars, in response to movement of the sections to an extended bed forming position, so as to tension the supporting springs and move the rods or bars into engagement with the underside of the associated mattress supporting fabric and thus effectively increase the biasing resistance to the sag under the weight of a bed occupant, as well as the tendency to sag towards the center of the bed.